You will be surprised to know that your skin is the largest part of the body. If it were laid out in one flat piece, it would cover an area of about 20 square feet. One small piece of skin contains all sorts of blood vessels, nerves, nerve endings plus over 100 sweat glands and three million cells.
The skin has two main layers – the outer layer called epidermis, the inner layer called dermis. The outer layer which can see and feel protects the body and helps control body temperature. Eyelids have the thinnest skin, with some light passing through them when they are closed. The skin on the back is the thickest, although the skin on feet and hands may be the toughest.
Skin is an important part of the immune system. It acts as a primary boundary between germs and the body. It is tough and generally impermeable to bacteria and viruses. The epidermis contains special cells that are an important early-warning component in the immune system. The skin also secretes antibacterial substances. These substances explain why we don't wake up in the morning with a layer of mold growing on the skin. Most bacteria and spores that land on the skin die quickly. Another role is its sensitivity to touch. The lower layers of the epidermis contain pigment, a coloring substance called melanin. This melanin determines the skin color.
Dermis is about twice as thick as epidermis. Oil glands in the dermis provide oils, the epidermis needs to keep the surface of the skin moist. Beneath the dermis are the sweat glands, each with a channel through the dermis to the surface of the epidermis. Waste products from the kidneys are released to the outside in the form of sweat. This is how the epidermis controls the body temperature.
Fat cells beneath the skin usually keep the skin smooth and rounded. A sudden loss of weight or gradual ageing of the body causes many of these cells to be absorbed to be used as energy.